Blends and structures based on ethylene vinyl alcohol copolymer and selected amorphous polyamides

ABSTRACT

A blend of 5 to 95 percent of an ethylene vinyl alcohol copolymer and 95 to 5 percent of an amorphous polyamide having fewer than about 0.100 equivalents of carboxyl end groups per kilogram of polyamide exhibits improved oxidative and thermal stability. The blend is useful for preparing films and multiple layered structures including thermoformed structures and oriented shrink films.

This is a division of application Ser. No. 07/551,389 filed Jul. 12,1990 now U.S. Pat. No. 5,126,402.

BACKGROUND OF THE INVENTION

This invention relates to a blend of ethylene vinyl alcohol copolymerand amorphous polyamide which provides thermoformable barrier layerswith improved resistance to thermal and oxidative degradation.

Blends of ethylene vinyl alcohol polymers with polyamides in general areknown, and have been used in packaging applications as barriers toinhibit the passage of atmospheric oxygen or other gases. Europeanpatent application 0 305 146 discloses a blend of about 70 to about 95percent by weight of an ethylene vinyl alcohol copolymer having acopolymerized ethylene content of about 20 to about 60 mole percent anda degree of saponification of at least about 90%, and about 5 to about30 percent by weight of an amorphous polyamide. The composition isuseful as a barrier layer in thermoformed containers.

European patent application 0 309 095 discloses a blend of about 50 toabout 95 weight percent of an amorphous polyamide and about 5 to about50 weight percent of a vinyl alcohol polymer having a copolymerizedethylene content of 0 to about 60 mol percent and a degree ofsaponification of at least about 90%. The blends have oxygen barrierproperties which are relatively independent of humidity. Packagingfilms, laminates, and containers prepared therefrom are disclosed.

Blends of ethylene vinyl alcohol ("EVOH") polymers with polyamides ingeneral are known, and have been used in packaging applications asbarriers to inhibit the passage of atmospheric oxygen or other gases.

Japanese patent application 53-49050 discloses a blend of ethylene vinylalcohol copolymer (EVOH) with 5 to 40 weight percent polyamide. The EVOHcontains 20-50 mole percent copolymerized ethylene, and is saponified atleast 90%. The polyamides disclosed include a copolymer of hexamethylenediamine with isophthalic and terephthalic acids, in mole ratios of 100/0to 50/50. The blend is formed into a film, which possesses gas barrierproperties. The barrier performance of the film is purported not todecline even in highly humid atmospheres.

U.S. Pat. No. 3,726,034 discloses mixtures of 70-99% polyamide and up to30% of a hydroxyl containing polyolefin. The polyamides consist oflinear unbranched polymer chains containing no additional functionalgroups. Exemplified are blends of nylon 6 and EVOH.

Japanese patent application 53-49050 discloses a blend of EVOH with 5 to40 weight percent polyamide. The polyamides include a copolymer ofhexamethylene diamine with isophthalic and terephthalic acids, in moleratios of 100/0 to 50/50. The blend is formed into a film, which is saidto possess excellent gas barrier properties.

U.S. Pat. No. 4,079,850 discloses a multilayer blow molded container,which contains a layer which may be EVOH, polyamide, or various blends,providing gas barrier properties. The polyamides which are mentioned arenylon 6, nylon 66, and nylon 12.

U.S. Pat. No. 4,427,825 discloses a composition of matter useful formaking films, of polyamide and 1-65% EVOH. Nylons with melting pointsgreater than 175° C. are preferred, such as nylon 11 or nylon 12.

U.S. Pat. No. 4,500,677 discloses a resin composition comprising amixture of two EVOH resins and a polyamide resin. The ratio of the EVOHresins to the nylon resin can be between 95:5 and 5:95. Nylon 6, nylon6,6 and other polyamides having linear alkylene groups are specificallymentioned.

In spite of the excellent barrier properties of ethylene vinyl alcoholpolymers, their use in blends has been limited to some extent because ofthe sensitivity of such polymers to thermal and oxidative degradation.In some instances blends of EVOH with polyamides have inadequatestability to degradation and gel formation. It is often observed thatthe melt viscosity of EVOH resins, whether alone or in a blend,increases with time, and the rate of increase increases withtemperature. It is presumed that this effect may result from impuritiesremaining from the manufacturing process or introduced during blending,including interactions between the EVOH and components introduced byblending. It is known, for example that acids catalyze crosslinkingreactions in EVOH, strong mineral acids such as HCl being especiallypotent. It is also possible that spontaneous dehydroxylation occurs atelevated temperatures, leading to interchain linkages. The resultingincrease in viscosity can eventually cause gelation or solidification ofthe molten polymer. Such behavior can result in metal surfaces ofprocessing equipment becoming coated with a varnish-like layer ofintractable, discolored, degraded polymer. Buildup of this layer cancause a gradual rise in torque required for extruder screws and, whenexfoliated, the sporadic appearance of gel particles in the extrudedproduct, particularly when regrind is included in the composition.Furthermore, when molten EVOH is exposed to oxygen, e.g. through airincursion at feed and vent ports of extruders, ethylene vinyl alcoholcopolymer can darken and crosslink to yellow-brown gel. As a result ofthese problems, comparatively low melt processing temperatures(210°-230° C.) are normally recommended for processing EVOH polymers,and even then such problems can persist.

There has been much activity to find a way to increase the thermal andoxidative stability of EVOH. As one example, British appln. 2,182,334discloses a vessel comprising a composition of EVOH and a propyleneresin or a thermoplastic resin having in the main or side chain acarbonyl group. The resin mixture is stabilized against gelation,discoloration, and reduction of gas barrier properties by incorporationof a hydroxide or higher fatty acid salt of an alkaline earth metal andan antioxidant.

U.S. Pat. No. 4,795,781 discloses a resin composition of saponifiedethylene/vinyl acetate copolymer containing terminal carboxyl (--COOH)and terminal amide (--COOR') groups, wherein the number (A) . of theterminal carboxyl groups and the number (B) of terminal amide groupssatisfies the relationship (B)/(A)+(B)×100≧5. The polyamide resin isobtained by N-substituted amide modification of the terminal carboxylgroup of the polyamide. It is preferable that the amount of the --COOHgroups not converted is not more than 50 microequivalents/g polymer.When the terminal carboxylic groups have been thus modified, troubles ofgel formation and of viscosity increasing are avoided. Suitablepolyamides include those prepared from a variety of dibasic acids,including terephthalic acid and isophthalic acid.

U.S. Pat. No. 4,747,744 discloses an improvement in pinhole resistanceor impact resistance in a resin composition of a saponified ethylenevinyl acetate and a polyamide having terminal end modification leavingcarboxylic end groups of 3×10⁻⁵ equivalent/g or less. During molding offilms, etc., there will occur no gelling or other trouble which willmake molding difficult, and the molded product has satisfactory gasbarrier properties. Suitable polyamides include nylon 6, nylon 610,nylon 12, etc.

The present invention provides a composition which has the desirableformability properties of blends of amorphous polyamides and EVOH,without suffering degradation in stability otherwise characteristic ofsuch blends.

SUMMARY OF THE INVENTION

The present invention provides a blend consisting essentially of:

(a) about 5 to about 95 percent by weight of at least one ethylene vinylalcohol copolymer having a copolymerized ethylene content of about 20 toabout 50 mole percent and a degree of saponification of at least about90%, and

(b) about 95 to about 5 percent by weight of a polyamide componentcomprising at least about 30 weight percent of at least one amorphouspolyamide having a glass transition temperature of up to about 160° C.and fewer than about 0.100 equivalents of carboxyl end groups perkilogram, said polyamide component forming a separate phase from that ofthe ethylene vinyl alcohol copolymer.

The present invention further provides films and multiple layeredstructures prepared from such blends and formed structures, includingthermoformed structures and oriented shrink films prepared therefrom.

DETAILED DESCRIPTION OF THE INVENTION

Materials and structures with barrier properties are important in manyapplications. Of particular interest are packaging materials which arebarriers to the penetration of gases, such as oxygen, carbon dioxide,and various aromas.

In many packaging applications EVOH resins are used as relatively thincomponents of multilayer structures or containers. Usually the majorparts of the structures are made of less expensive "structural"materials, bound to the EVOH layer by adhesive layers. The fabricationprocess in converting multilayer structures into final products ofteninvolves a mechanical deformation operation, such as orientation,thermoforming, or stretching in general, depending on the final form ofthe desired structure. However, EVOH generally exhibits very poordrawability, that is, the ability to be stretched or deformed uniformlyat a temperature below its melting point. Quite often the stretching ordeformation operation induces cracks, discontinuity or thinning("neckdown") in the EVOH layer. As a result stretched or deformedmultilayer structures which include a layer of EVOH resin often exhibitinferior barrier properties. If an amorphous polyamide is added toimprove the drawability, however, the thermal and oxidative stabilityproperties may suffer.

For the purposes of this invention, a deformation process includes anyprocess for forming a shaped article (e.g., a film or a container) which(a) is distinct from the initial melt processing step and (b) which isperformed at a temperature which is elevated above room temperature butlower than the melting point of the polymeric structural material.Casting of a film would not be a deformation process according to thisdefinition because it is a melt processing step; vacuum-forming a filmto prepare a container would be a deformation process. Making a film bya blown tubular process may or may not be a deformation process,depending on the temperature of the tubing or bubble at the locationwhere blowing occurs. Examples of deformation processes includethermoforming (but excluding melt phase thermoforming), vacuum-forming,solid phase pressure forming, co-injection blow molding, co-injectionstretch blow molding, tube extrusion followed by stretching, scraplessforming, forging, and tubular or flat sheet oriented film processes.Examples of articles that can be prepared using deformation processesare films and containers such as bottles, jars, cans, bowls, trays,dishes, pouches, oriented films, and shrink films. Deformation ofpolymeric materials is not only a way to attain such final shapedarticles, but may also be a means to enhance barrier properties,mechanical properties, or even optical properties.

The temperature of the deformation step is usually determined by the"forming temperature" of the structural material, that is, thetemperature at which it can be deformed. The forming temperature of apolymer is not readily related to any material properties of thepolymer, except that it is normally higher than the Tg of the polymer.In addition, this temperature is affected by the magnitude and rate ofdeformation of the particular process employed. The forming temperatureof a given material for a given process can be readily determined by aperson skilled in the art with a minimum of experimentation. Manystructural materials have a lower forming temperature than that of EVOH,and it may be desirable for many reasons to conduct a molding operationat as low a temperature as possible. Furthermore, it may be desirable toreach an extent of deformation as high as possible. Thus thetemperatures used for the deformation of such multilayer structures maybe so low or the extent of deformation may be so high that thedrawability of the EVOH layer is exceeded. As a consequence the desireddeformed articles cannot be made without tearing or rupturing of theEVOH layer. The resulting discontinuities in the EVOH layer result ininferior oxygen barrier performance of the resulting article. An objectof this invention is to provide a modified EVOH composition which may beused in deformed multilayer structures to avoid the above mentionedproblems, and without substantially sacrificing the excellent gasbarrier properties of EVOH or causing undue oxidative or thermaldegradation.

The first component cf the composition of the present invention is anethylene vinyl alcohol copolymer. The EVOH resins useful in thisinvention include resins having a copolymerized ethylene content ofabout 20 to about 60 mole %, especially about 25 to about 50 mole %.Copolymers of lower than about 15 to 20 mole % ethylene tend to bedifficult to extrude while those above about 60 or 65 mole % ethylenehave reduced oxygen barrier performance. These polymers will have asaponification degree of at least about 90%, especially at least about95%. A degree of saponification of less than about 90% results ininferior oxygen barrier properties. The ethylene vinyl alcohol copolymermay include as an optional comonomer other olefins such as propylene,butene-1, pentene-1, or 4-methylpentene-1 in such an amount as to notchange the inherent properties of the copolymer, that is, usually in anamount of up to about 5 mole % based on the total copolymer. The meltingpoints of these ethylene vinyl alcohol polymers are generally betweenabout 160° and 190° C.

Ethylene vinyl alcohol polymers are normally prepared bycopolymerization of ethylene with vinyl acetate, followed by hydrolysisof the vinyl acetate component to give the vinyl alcohol group. Thisprocess is well known in the art.

The second component of the present invention is at least one selectedamorphous polyamide. The polyamide component comprises about 5 to about95 percent by weight of the total composition of EVOH plus polyamide,preferably about 10 to about 35 percent, and most preferably about 15 toabout 30 percent.

The term "amorphous polyamide" is well known to those skilled in theart. "Amorphous polyamide," as used herein, refers to those polyamideswhich are lacking in crystallinity as shown by the lack of an endothermcrystalline melting peak in a Differential Scanning Calorimeter ("DSC")measurement (ASTM D-3417), 10° C./minute.

Examples of the amorphous polyamides that can be used include thoseamorphous polymers prepared from the following diamines:hexamethylenediamine, 2-methylpentamethylenediamine,2,2,4-trimethylhexamethylenediamine,2,4,4-trimethylhexamethylenediamine, bis(4-aminocyclohexyl)methane,2,2-bis(4-aminocyclohexyl)isopropylidine, 1,4-diaminocyclohexane,1,3-diaminocyclohexane, meta-xylylenediamine, 1,5-diaminopentane,1,4-diaminobutane, 1,3-diaminopropane, 2-ethyldiaminobutane,1,4-diaminomethylcyclohexane, p-xylylenediamine, m-phenylenediamine,p-phenylenediamine, and alkyl substituted m-phenylenediamine andp-phenylenediamine.

Examples of polyamides that can be used include those amorphous polymersprepared from the following dicarboxylic acids: isophthalic acid,terephthalic acid, alkyl substituted iso- and terephthalic acid, adipicacid, sebacic acid, butane dicarboxylic acid, and the like.

Polyamides prepared from aromatic diamines and aromatic diacids are alsoknown. However, certain of these all-aromatic polyamides are known to beintractable under ordinary melt processing conditions, and thus are notnormally suitable. Thus the preferred amorphous polyamides are those inwhich either the diamine or the diacid moiety is aromatic, and the othermoiety is aliphatic. The aliphatic groups of these polyamides preferablycontain 4-8 carbon atoms in a chain or an aliphatic cyclic ring systemhaving up to 15 carbon atoms. The aromatic groups of the polyamidespreferably have mono or bicyclic aromatic rings which may containaliphatic substituents of up to about 6 carbon atoms.

However, not all of these aromatic/aliphatic combinations willnecessarily provide suitable amorphous polyamides. For example,specifically metaxylylenediamine adipamide is not generally suitable forthis invention. This polymer readily crystallizes under heatingconditions typical for thermoforming operations, and also crystallizesupon orienting. This illustrates the fact that it is important todetermine that a particular polyamide is amorphous, and not to relysolely on the chemical structure of the polymer. This determination caneasily be made by DSC.

Specific examples of amorphous polyamides which may be suitable for thisinvention include: hexamethylenediamine isophthalamide,hexamethylenediamine isophthalamide/terephthalamide terpolymer, havingiso/terephthalic moiety ratios of 100/0 to 60/40, mixtures of 2,2,4- and2,4,4-trimethylhexamethylenediamine terephthalamide, copolymers ofhexamethylene diamine and 2-methylpentamethylenediame with iso- orterephthalic acids, or mixtures of these acids. Polyamides based onhexamethylenediamine iso/terephthalamide containing high levels ofterephthalic acid moiety may also be useful provided a second diaminesuch as 2-methyldiaminopentane is incorporated to produce a processibleamorphous polymer.

Polyamides prepared from aliphatic diamines with aliphatic diacids arethe traditional semicrystalline nylons (also referred to as crystallinenylons) and are not amorphous polyamides. Many such semicrystallinenylon, particularly those having comparatively short carbon chains (suchas nylon 6) are, in addition, completely miscible with EVOH and thus donot, by themselves, form the two-phase structure characteristic of thepresent invention.

The above amorphous polyamides, however, may contain as comonomers minoramounts of lactam species such as caprolactam or lauryl lactam, eventhough polymers prepared from on such monomers alone would not beamorphous. The important feature is that the polyamide as a whole isamorphous. Thus small amounts of these comonomers may be incorporated aslong as they do not impart crystallinity to the polyamide. Similarly,limited amounts of semicrystalline nylons may be present along with theselected amorphous polyamide in blends of the present invention providedthey are at levels which do not seriously interfere with the stabilityof the composition or cause the composition to become a single phase.But blends in which the amorphous polyamide is entirely replaced with asemicrystalline nylon do not exhibit the present improvement instability, even when the acid end groups of the nylon fall within thelimits defined below. Compositions may be suitable in which asemicrystalline nylon comprises about 0 to about 70 percent of the totalpolyamide component, although preferably the semicrystalline nylon islimited to about 10 to 40 or preferably about 20 to about 40 percent.

For most applications the Tg of the amorphous polyamide (as measured inthe dry state, i.e., containing about 0.12 weight % moisture or less)should be in the range of about 60° C. to about 160° C., and preferablyabout 80° C. to about 130° C. Certain unblended amorphous polyamides, asdescribed above, have Tg_(s) of around 125° C. when dry. The lower limiton T_(g) is not clearly demarked and is not believed to be critical; 60°C. is an approximate lower limit. The upper limit on the T_(g) islikewise not clearly demarked. But amorphous polyamides with T_(g) aboveabout 160° C. are not easily processable readily thermoformable whenused as a barrier layer. Thus all-aromatic polyamides, having aromaticgroups in both acid and amine moieties, tend to have a T_(g) which istoo high to permit thermoforming, and are thus normally unsuitable forthe purposes of this invention. As a secondary consideration, themolecular weight of the amorphous polyamide should be in a suitablerange for ease of processing, yet not so low that the final product isbrittle. Suitable molecular weights correspond approximately to anintrinsic viscosity (I.V.) of 0.5 to 0.95.

While amorphous polyamides in general provide ease of thermoforming toblends of ethylene vinyl alcohol copolymers, in many cases the thermalor oxidative stability of the blends are not as good as desired. Forexample, on extended heating the melt index of such blends may decreasedramatically and gel formation may occur. It has now been found that useof a select group of amorphous polyamides avoids this problem.Specifically, amorphous polyamides having less than about 100milli-equivalents of terminal carboxyl groups per kilogram of polyamideare suitable, and those amorphous polyamides having less than about 85or preferably less than about 55 milli-equivalents per kilogram arepreferred. When such polyamides are used the blends exhibitsignificantly improved stability.

Normally polyamides will have a certain number of both acid and amineend groups derived from their diacid and diamine monomeric components.Commercially available amorphous polyamides typically have acid endgroups in excess of 100 meq/kg of polymer. One method of preparingpolyamides with the desired low level of such acid end groups involvescarefully controlling the polymerization conditions. For example, asuitable amorphous polyamide may be prepared by mixinghexamethylenediamine with an appropriate amount of isophthalic andterephthalic acids in water to form the salt, adjusting the pH of thesolution to about 8-9. (Very minor amounts of e.g. wax, inorganic acidcatalyst, and antifoaming agent may also be added at this point.)

The acid and amine end groups in the final polymer can be controlled byknown processes, for example, by addition of additional difunctional ormonofunctional amines to shift the balance between acid and amine enddistribution. There are many suitable difunctional amines, one of whichis additional hexamethylenediamine; suitable monofunctional aminesinclude octadecyl amine, benzyl amine, and others that will be apparentto one skilled in the art. (Small amounts of monofunctional acids suchas acetic acid or stearic acid may also be added to control molecularweight.) The composition thus prepared is further polymerized e.g. in anautoclave at 280°-295° C. by known methods to form the final low-acidpolymer.

The level of carboxyl end groups in a polyamide can be measured bydissolving a sample of the polymer in hot benzyl alcohol, followed byhot titration of the carboxyl groups with sodium hydroxide, usingphenolphthalein indicator. Amine end groups can be analyzed bydissolving the polyamide in a hot mixture of 85% phenol and 15%methanol, followed by potentiometric titration with perchloric acid.

While not wishing to be bound by any theory, it is speculated that muchof the thermal instability of blends of EVOH with amorphous polyamidesis caused by acid-catalyzed reactions in the EVOH, due to the acid endgroups of the polyamide. It is surprising that this effect should beimportant, because it would be expected that most of the end groupswould be located within the separate domains of the amorphous polyamide.Any deleterious interaction with the EVOH would be expected to occuronly at the interface of the EVOH and polyamide domains and should thusnot be of great importance. It is speculated that many of thedeleterious acid end groups in the amorphous polyamide may be actuallylocated on low molecular weight polyamide oligomers which can diffuseinto the EVOH material and cause deterioration. Preparation of theamorphous polyamide as described above may reduce the number of suchcomparatively active and mobile acid end groups to a safe level.

In addition to the above-described components, up to about 10 weight %of a liquid or solid plasticizer such as glycerol, sorbitol, mannitol,or aromatic sulfonamide compounds such as toluenesulfonamide("Santicizer 8" from Monsanto) may be included with the amorphouspolyamide. Customary amounts of antioxidants may also be employed.

Blends of the present invention can be made by traditional melt blendingprocesses such as extrusion mixing. Films and multiple layer structurescan be prepared by traditional process such as extrusion, coextrusion,lamination, blow molding, etc. Other formed articles can be made by thedrawing, stretching, and thermoforming process described above.

The blends and structures of the present invention are useful whereoxygen and/or flavor barrier properties and good adhesion properties aredesired, e.g., in coextruded plastic structures, such as multilayersheets and thermoformed containers therefrom, multilayer films includingshrink films, pipes, tubes, blow-molded articles, and multilayerstructures including thermoformed structures, in particular containers,particularly for food packaging applications. When thermoformedstructures are prepared, at least one layer will preferably be preparedfrom a structural polymer such as polybutylene, polypropylene,polypropylene copolymers with ethylene, polyethylene, polyethylenecopolymers, copolymers of ethylene with vinyl acetate, copolymers ofethylene with carboxylic acids wherein the carboxylic acid isunneutralized or is neutralized to form an ionomer, polyethyleneterephthalate, polymers based on vinyl chloride, polymers based onstyrene, and blends of such polymers.

EXAMPLES 1-7 AND COMPARATIVE EXAMPLES C1-C5

The thermal stability of blends of ethylene vinyl alcohol copolymer withcertain amorphous polyamides was determined using a series of tests.Blends were prepared from 80 percent by weight ethylene vinyl alcoholcopolymer containing 30 mole % copolymerized ethylene, melt index 3dg/min, >99% saponification and 20 percent by weight of a polyamide. InExamples 1-7 the polyamides were amorphous polyamides prepared bycondensation of hexamethylenediamine with 70% isophthalio acid and 30%terephthalic acid, (denoted "APA") having an inherent viscosity asindicated in the Table. (Inherent viscosity of the polyamide isdetermined by dissolving the polymer in hot m-cresol followed byviscosity measurement using a Schott Autoviscometer.) The polyamides,prepared by the method described above, had a level of acid end groupscorresponding to less than 100 milli-equivalents/kg polyamide, asindicated in the Table. In Comparative Example C1 the polyamide was acommercial sample believed to be a similar isophthalic/terephthaliccopolymer having IV and end group distribution as shown; in ComparativeExample C2 the polyamide was of the same composition except having ahigher acid group concentration, and in Comparative Example C3 thepolyamide had yet a higher acid end group concentration. For ComparativeExample C4 a semicrystalline nylon, nylon 6 (polycaprolactam) was used,which did have a comparatively low level of acid end groups. Blendingand mixing of the samples was accomplished on an extruder, followed bypelletization.

After blending, the thermal stability of the compositions was evaluatedby subjecting the samples to Haake mixing. In a typical run, a sample of50 grams was mixed in a Haake mixer (Haake Buchler Instruments, Inc.,Rheocord™ System 40), at 230° C. for 30 minutes and 50 r.p.m. The barreltemperature was set at 230° C., however, the melt temperature generallyreached 240° to 250° C. due to sheer energy. The torgue (in meter-grams)at the end of the mixing is reported in Table I. (An increase in torquecompared to the control sample, C5, suggests a crosslinking reaction.)The melt flow index (in dg/min, run at 230° C. after a 5 minute heatingtime) and the gel content of the sample after Haake treatment are alsoreported. The gel content was measured by dissolving 10 g of the samplein a mixture of 50:50 water:isopropanol at about 70° C. The gel wasobtained by filtering the solution through a 200 mesh (0.074 mm) screen(for Examples 1-6 and Comparative Example C5) or a 100 mesh (0.14 mm)screent (for Comparative Examples C1-C3), to retain the dissolved gel.After drying, the gel content was calculated. The results in Table Ishow that the compositions of the present invention exhibit muchimproved thermal stability compared with examples in which either apolyamide having greater than 100 milli-equivalents acid end groups wasused, or in which a semicrystalline nylon alone was blended with EVOH.

                  TABLE I                                                         ______________________________________                                        Polyamide.sup.a     Melt                                                             IV ends: acid amine                                                                        index    Haake   Gel                                      Ex   Type             (meg/kg)                                                                              after heat                                                                           Torque                                                                              %                                  ______________________________________                                        1    APA     0.89     85   62   1.44   510   0.38                             2    "       0.85     49   88   2.10   480   0.33                             3    "       0.83     48   88   1.97   460   0.58                             4    "       0.76     54   90   2.56   450   0.16                             5    "       0.73     29   93   2.25   420   0.22                             6    "       0.68     44   102  2.67   490   0.24                             7.sup.b                                                                            "       0.71     28   103  1.30   326   c                                C1   "       0.87     163  27   0.11   885   14.80                            C2   "       0.82     150  31   0.14   800   5.96                             C3   "       0.76     d    31   0.11   720   6.27                             C4   nylon6  68.sup.e 45   52   0      1380  c                                                                (no flow)                                     C5.sup.f                                                                           none    (EVOH    --   --   2.10   534   0.23                                          only)                                                            ______________________________________                                         .sup.a All examples except as noted are blends of EVOH and polyamide in a     80/20 weight ratio.                                                           .sup.b EVOH and polyamide in a 35/65 weight ratio.                            c Not measured.                                                               .sup.d Measured value of 96 is believed to be erroneously low. Estimated      value is above 120, based on method of preparation.                           .sup.e Relative viscosity of 8.4 wt. % solution in 90% formic acid.           .sup.f Control example with no polyamide.                                

EXAMPLE 8

The blend composition of Example 4 was coextruded into a five layersheet. The core layer (the blend of Example 4), 0.15 mm thick, wasextruded using a 38 mm single extruder. Two surface layers,polypropylene homopolymers with a melt flow index of 2.0 (ASTM D-1238Condition L), each 0.6 to 0.7 mm thick, were extruded on two separatesingle screw extruders, one 50 mm and the other 63.5 mm. Two adhesivelayers, 0.05 to 0.07 mm thick, maleic anhydride grafted copolymer ofpropylene and ethylene, melt flow index 4.5 and melting point I44.C,were extruded on a 50 mm single extruder. The multiple layer sheet wascast onto rolls cooled with water having a temperature of about 90° C.

Subsequently the cast multilayer sheet was thermoformed by solid statepressure forming on a Labform™ apparatus (Hydrotrim Co.) intocylindrical, can-shaped containers, 85 mm diameter and 127 mm deep. Thesheet samples were heated by ceramic heaters at 320° to 380° C.; thesheet samples attained a temperature of 135° to 155™° C. Forming wasaccomplished using plug assist air pressure of 480 kPa. The formedcontainers were free from defects by visual examination, and microscopicexamination of the cross section of the container sidewalls, cutperpendicular to the axis, revealed a uniform core layer.

What is claimed is:
 1. A multiple layer structure wherein at least oneof the layers is prepared from a blend consisting essentially of:(a)about 5 to about 95 percent by weight of at least one ethylene vinylalcohol copolymer having a copolymerized ethylene content of about 20 toabout 50 mole percent and a degree of saponification of at least about90%, and (b) about 95 to about 5 percent by weight of a polyamidecomponent comprising at least about 30 weight percent of at least oneamorphous polyamide having a glass transition temperature of up to about160° C. and fewer than about 0.100 equivalents of carboxyl end groupsper kilogram, said polyamide component forming a separate phase fromthat of the ethylene vinyl alcohol copolymer.
 2. The multiple layerstructure of claim 1 wherein the at least one amorphous polyamidecomprises about 100 weight percent of the polyamide component.
 3. Themultiple layer structure of claim 1 wherein the polyamide componentfurther comprises 0 to about 70 percent by weight of a semicrystallinepolyamide.
 4. The multiple layer structure of claim 1 wherein thepolyamide component has fewer than about 0.055 equivalents of carboxylend groups per kilogram of polyamide.
 5. The multiple layer structure ofclaim 1 wherein the at least one ethylene vinyl alcohol copolymercontains about 25 to about 50 mole percent copolymerized ethylene andhas a degree of saponification of at least about 95%.
 6. The multiplelayer structure of claim 1 wherein the at least one amorphous polyamideis selected from the group consisting of hexamethylenediamineisophthalamide, hexamethylenediamine isophthalamide/terephthalamideterpolymer, having isophthalic/terephthalic moiety ratios of 100/0 to60/40, mixtures of 2,2,4- and 2,4,4-trimethylhexamethylenediamineterephthalamide, copolymers of hexamethylenediamine and2-methylpentamethylenediamine with iso- or terephthalic acids, ormixtures of these acids.
 7. The multiple layer structure of claim 1wherein the at least one of the layers is a structural polymer.
 8. Themultiple layer structure of claim 7 wherein the structural polymer isselected from the group consisting of polybutylene, polypropylene,polypropylene copolymers with ethylene, polyethylene, polyethylenecopolymers, copolymers of ethylene with vinyl acetate, copolymers ofethylene with carboxylic acids wherein the carboxylic acid isunneutralized or is neutralized to form an ionomer, polyethyleneterephthalate, polymers based on vinyl chloride, polymers based onstyrene, and blends of such polymers.
 9. A formed structure prepared bythermoforming the multiple layer structure cf claim
 7. 10. The formedstructure of claim 9 in the form of a container.
 11. The multiple layerstructure of claim 1 in the form of a biaxially oriented film.
 12. Themultiple layer structure of claim 1 in the form of an oriented shrinkfilm.